Transducer assembly for an ultrasonic fluid meter

ABSTRACT

A transducer assembly for an ultrasonic fluid meter. At least some of the illustrative embodiments are transducer assemblies comprising an elongated outer housing defining an interior and an exterior, the elongated outer housing having an axis along its elongated direction, a piezoelectric element coupled to and at least partially occluding a first end of the elongated outer housing, a pin holder coupled to and at least partially occluding a second end of the elongated outer housing, the pin holder comprising a first electrical pin, and a first wire coupling the first electrical pin to the piezoelectric element (wherein the first wire runs through the interior of the elongated outer housing).

CROSS REFERENCE TO RELATED APPLICATIONS

This specification claims the benefit of provisional patent applicationSer. No. 60/707,814 filed Aug. 12, 2005. This specification also claimsthe benefit of provisional application Ser. No. 60/710,068 filed Aug.22, 2005. Each of these applications are incorporated by referenceherein as if reproduced in full below.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Various embodiments of the invention relate to ultrasonic flow meters.

2. Description of the Related Art

After hydrocarbons have been removed from the ground, the fluid stream(such as crude or natural gas) is transported from place to place viapipelines. It is desirable to know with accuracy the amount of fluidflowing in the stream, and particular accuracy is demanded when thefluid is changing hands, or “custody transfer.” Even where custodytransfer is not taking place, however, measurement accuracy isdesirable.

Ultrasonic flow meters may be used in situations such as custodytransfer. In an ultrasonic flow meter, ultrasonic signals are sent backand forth across the fluid stream to be measured, and based on variouscharacteristics of the ultrasonic signals, a fluid flow may becalculated. Mechanisms which improve the quality of the ultrasonicsignals imparted to the fluid may improve measurement accuracy.Moreover, ultrasonic flow meters may be installed in harsh environments,and thus any mechanism to reduce maintenance time, and if possible,improve performance, would be desirable.

SUMMARY

The problems noted above are addressed, at least in part, by atransducer housing for an ultrasonic fluid meter. At least some of theillustrative embodiments a transducer housing comprising a housinghaving a proximal end, a distal end and an internal volume, the housingcouples to a spoolpiece of an ultrasonic meter, and an acoustic matchinglayer that fluidly seals the distal end from the internal volume(wherein the housing accepts a piezoelectric element within the internalvolume and proximate to the acoustic matching layer). The acousticmatching layer has an acoustic impedance between that of thepiezoelectric element and a fluid within the ultrasonic meter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of embodiments of the invention,reference will now be made to the accompanying drawings, wherein:

FIG. 1A is an elevational cross-sectional view of an ultrasonic flowmeter;

FIG. 1B is an elevational end view of a spoolpiece which illustrateschordal paths M, N, O and P;

FIG. 1C is a top view of a spoolpiece housing transducer pairs;

FIG. 2 illustrates an assembly in accordance with embodiments of theinvention;

FIG. 3 illustrates a perspective cross-sectional view of a transducerhousing in accordance with embodiments of the invention;

FIG. 4 illustrates an elevational cross-sectional view of a transducerhousing in accordance with embodiments of the invention;

FIG. 5 illustrates an integrated transducer assembly in accordance withembodiments of the invention;

FIG. 6 illustrates a perspective cross-sectional view of an integratedtransducer assembly in accordance with embodiments of the invention;

FIG. 7A illustrates a perspective view of the front face of apiezoelectric element in accordance with embodiments of the invention;

FIG. 7B illustrates a perspective view of the back face of apiezoelectric element in accordance with embodiments of the invention;and

FIG. 8 is a flow diagram illustrating methods of replacing a transducerassembly in accordance with embodiments of the invention.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. This document does not intendto distinguish between components that differ in name but not function.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . ”. Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection, or through anindirect connection via other devices and connections.

“Fluid” shall mean a liquid (e.g., crude oil or gasoline) or a gas(e.g., methane).

DETAILED DESCRIPTION

FIG. 1A is an elevational cross-sectional view of an ultrasonic meter101 in accordance with embodiments of the invention. Spoolpiece 100,suitable for placement between sections of a pipeline, is the housingfor the meter 101. The spoolpiece 100 has an internal volume that is aflow path for a measured fluid and also has a predetermined size thatdefines a measurement section within the meter. A fluid may flow in adirection 150 with a velocity profile 152. Velocity vectors 153-158illustrate that the fluid velocity through spoolpiece 100 increasestoward the center.

A pair of transducers 120 and 130 is located on the circumference of thespoolpiece 100. The transducers 120 and 130 are accommodated by atransducer port 125 and 135, respectively. The position of transducers120 and 130 may be defined by the angle θ, a first length L measuredbetween transducers 120 and 130, a second length X corresponding to theaxial distance between points 140 and 145, and a third length Dcorresponding to the pipe diameter. In most cases distances D, X and Lare precisely determined during meter fabrication. Further, transducerssuch as 120 and 130 may be placed at a specific distance from points 140and 145, respectively, regardless of meter size (i.e. spoolpiece size).Although the transducers are illustrated to be recessed slightly, inalternative embodiments the transducers protrude into the spoolpiece.

A path 110, sometimes referred to as a “chord,” exists betweentransducers 120 and 130 at an angle θ to a centerline 105. The length Lof “chord” 110 is the distance between the face of transducer 120 andthe face of transducer 130. Points 140 and 145 define the locationswhere acoustic signals generated by transducers 120 and 130 enter andleave fluid flowing through the spoolpiece 100 (i.e. the entrance to thespoolpiece bore).

Transducers 120 and 130 are preferably ultrasonic transceivers, meaningthat they both generate and receive ultrasonic signals. “Ultrasonic” inthis context refers to frequencies above about 20 kilohertz. To generatean ultrasonic signal, a piezoelectric element is stimulatedelectrically, and it responds by vibrating. The vibration of thepiezoelectric element generates an ultrasonic signal that travelsthrough the fluid across the spoolpiece to the corresponding transducerof the transducer pair. Similarly, upon being struck by an ultrasonicsignal, the receiving piezoelectric element vibrates and generates anelectrical signal that is detected, digitized, and analyzed byelectronics associated with the meter. Initially, downstream transducer120 generates an ultrasonic signal that is then received by upstreamtransducer 130. Some time later, the upstream transducer 130 generates areturn ultrasonic signal that is subsequently received by the downstreamtransducer 120. Thus, the transducers 120 and 130 play “pitch and catch”with ultrasonic signals 115 along chordal path 110. During operation,this sequence may occur thousands of times per minute.

The transit time of the ultrasonic signal 115 between transducers 120and 130 depends in part upon whether the ultrasonic signal 115 istraveling upstream or downstream with respect to the fluid flow. Thetransit time for an ultrasonic signal traveling downstream (i.e. in thesame direction as the flow) is less than its transit time when travelingupstream (i.e. against the flow). The upstream and downstream transittimes can be used to calculate the average flow velocity along thesignal path, and may also be used to calculate the speed of sound in thefluid. Knowing the cross-sectional area of the meter carrying the fluidand assuming the shape of the velocity profile, the average flowvelocity over the area of the meter bore may be used to find the volumeof fluid flowing through the meter 101.

Ultrasonic flow meters can have one or more pairs of transducerscorresponding to one or more paths. FIG. 1B is an elevational end viewof a spoolpiece having a diameter D. In these embodiments, spoolpiece100 comprises four chordal paths M, N, O, and P at varying levelsthrough the fluid flow. Each chordal path M-P corresponds to twotransducers behaving alternately as a transmitter and receiver. Alsoshown are control electronics 160, which acquire and process data fromthe four chordal paths M-P. Hidden from view in FIG. 1B are the fourpairs of transducers that correspond to chordal paths M-P.

The precise arrangement of the four pairs of transducers may be furtherunderstood by reference to FIG. 1C. In some embodiments, four pairs oftransducer ports are mounted on spoolpiece 100. Each pair of transducerports corresponds to a single chordal path of FIG. 1B. A first pair oftransducer ports 125 and 135 houses transducers 120 and 130 (FIG. 1A).The transducers are mounted at a non-perpendicular angle θ to centerline105 of spool piece 100. Another pair of transducer ports 165 and 175(only partially in view) house associated transducers so that thechordal path loosely forms an “X” with respect to the chordal path oftransducer ports 125 and 135. Similarly, transducer ports 185 and 195may be placed parallel to transducer ports 165 and 175 but at adifferent “level” (i.e. a different elevation in the spoolpiece). Notexplicitly shown in FIG. 1C is a fourth pair of transducers andtransducer ports. Taking FIGS. 1B and 1C together, the pairs oftransducers are arranged such that the upper two pairs of transducerscorresponding to chords M and N, and the lower two pairs of transducerscorresponding to chords O and P. The flow velocity of the fluid may bedetermined at each chord M-P to obtain chordal flow velocities, and thechordal flow velocities combine to determine an average flow velocityover the entire pipe. Although four pairs of transducers are shownforming an X shape, there may be more or less than four pairs. Also, thetransducers could be in the same plane or in some other configuration.

FIG. 2 illustrates an assembly 200 that couples to and/or within thetransducer ports (e.g., 165, 175 of FIG. 1C). In particular, theassembly 200 comprises a wiring harness 202 having a connector 204 on adistal end 205 thereof. The wiring harness 202, and in particularconnector 204, couple to a transducer port (not shown in FIG. 2) by wayof a retaining nut 206 and transducer housing 208. The transducerassembly 210 electrically couples to the connector 204 of the wiringharness 202, and therefore the meter electronics, through an aperture inthe retaining nut 206. The transducer assembly 210 telescopes into thetransducer housing 208 and is held in place, at least in part, by theretaining nut 206. When the transducer assembly 210 and transducerhousing 208 are engaged, a piezoelectric element 214 of the transducerassembly 210 acoustically couples to a matching layer 212. Thetransducer housing 208 and the transducer assembly 210 are eachdiscussed in turn.

FIG. 3 shows a perspective cross-sectional view of a transducer housing208 in accordance with embodiments of the invention. The housing 208comprises a proximal end 318, distal end 302, and an internal volume310. The distal end 318 is at least partially occluded by the acousticmatching layer 212. The acoustic matching layer 212 seals the distal end302, and the exterior side 314 of the matching layer 212 is exposed tofluids flowing through the spoolpiece/meter (FIGS. 1A-C). Threads 306 onthe outside diameter of the transducer housing 208 allow the housing 208to be coupled to the spoolpiece (FIGS. 1A-C), and o-rings 308 seal thehousing 208 to the transducer port (FIGS. 1A-C). In alternativeembodiments, the transducer housing 208 is welded to the transducer port(FIGS. 1A-C) of the spoolpiece.

In some embodiments, the transducer housing 208 is metal such as lowcarbon stainless steel. In alternative embodiments any material capableof withstanding the pressure of the fluid within the meter, such as highdensity plastics or composite materials, may be equivalently used. Insome embodiments the wall thickness of the transducer housing 208 isselected to compress slightly in response to the differential pressurebetween the fluid in the meter and the internal volume 310. Thecompression of the walls of the transducer housing 208 in theseembodiments aids in holding the acoustic matching layer 212 in place.For example, the wall behind the acoustic matching layer deflects inwardslightly, and the smaller inside diameter provides support to theacoustic matching layer to resist the lateral movement caused by theforces of fluid pressure within the meter. Moreover, during the processof bonding the acoustic matching layer 212 to the transducer housing208, the housing 208 is stretched (within the elastic limit of the wallmaterial) to accept the acoustic matching layer 212.

To aid in bonding the acoustic matching layer 212 to the transducerhousing 208, in some embodiments the acoustic matching layer 212 has ameniscus 304 around the edge on the interior side 312. FIG. 4illustrates an elevational cross-sectional view of the transducerhousing 208 which further illustrates the meniscus 304 in accordancewith these embodiments. In particular, the meniscus 304 of the acousticmatching layer 212 increases the contact area between the transducerhousing wall and the acoustic matching layer 212, but preferably leavessufficient surface area on the interior side 312 of the acousticmatching layer 212 to allow acoustic coupling between the piezoelectricelement of the transducer assembly (not shown in FIG. 4). Thus, thetransducer assembly 210 provides a space for the meniscus 304 to ensurethat the meniscus 304 does not interfere with the coupling of thepiezoelectric element to the matching layer 212.

The material of the acoustic matching layer 212 is one or more selectedfrom the group: glass; ceramic; plastic; glass-filled plastic; orcarbon-fiber filled plastic. Although some embodiments use 100% glass asthe acoustic matching layer, alternative embodiments using plastic couldhave a glass content of 30% or less. Regardless of the material of theacoustic matching layer, the acoustic matching layer 212 providesacoustical coupling between the piezoelectric element 214 and fluid inthe meter. In accordance with embodiments of the invention, the acousticmatching layer has an acoustic impedance between that of thepiezoelectric element 214 and fluid within the meter. With the acousticimpedance of the matching layer between that of the piezoelectricelement and the fluid in the meter, the quality of the ultrasonic signalis improved (e.g., larger amplitude and faster rise time). Glass is thepreferred material for the acoustic matching layer since it has thedesired acoustic impedance to provide good acoustic coupling while beingstrong enough to resist the pressure of the fluid within the meter sothat the piezoelectric element can be isolated from the fluid in thewithin the meter. Comparatively, the acoustic impedance of a matchinglayer comprising substantially stainless steel is more than the acousticimpedance of the piezoelectric element, and therefore provides pooracoustic coupling. In some embodiments the acoustic impedance of theacoustic matching layer 212 is between about 1 and about 30 Mega-rayl(MRayl); or alternatively, between about 10 and about 15 MRayl.

When a transducer assembly 210 is inserted into the transducer housing208, the piezoelectric element 214 (FIG. 2) of the transducer assembly210 abuts the interior side 312 of the acoustic matching layer 212. Toprovide good acoustic coupling, the interior 312 and exterior 314 facesof the acoustic matching layer 212 are substantially flat andsubstantially parallel to one another. In some embodiments, the facesare flat to within 0.001 inch or better and parallel to within 0.003inches or better. Additionally, the transducer assembly 210 ispositioned such that the piezoelectric element 214 is centered againstthe acoustic matching layer 212. Transducer housings 208 with acousticmatching layers as discussed herein may be manufactured by and purchasedfrom Dash Connector Technology of Spokane Wash.

The acoustic matching layer 212 has a thickness (along an axis sharedwith the remaining portions of the transducer housing 208) that in someembodiments is substantially equal to an odd multiple of one-quarter (¼,¾, 5/4, 7/4, etc.) wavelength of the sound generated by thepiezoelectric element 214. For example, consider a piezoelectric element214 operating at a frequency of 1 MHz and an acoustic matching layer 212with a speed of sound of 5,000 m/s. The wavelength of the sound in thematching layer is approximately 0.197 inches. In these embodiments theacoustic matching layer may be 0.049, 0.148, 0.246, 0.344, and so on,inches thick. A thinner acoustic matching layer gives better acousticalperformance, but making the acoustic matching layer thicker enables thetransducer housing 208 to withstand higher pressures. Picking theoptimal matching layer thickness involves choosing the thinnest matchinglayer that can hold the highest pressures expected inside the meter.

To reduce electrical noise and double the drive voltage, it is oftendesirable to electrically connect the piezoelectric elementdifferentially (discussed below), which means the portion of thepiezoelectric element that abuts the acoustic matching layer may have anelectrically conductive coating. If the acoustic matching layer ismetallic, a thin electrical insulator is used between the metal andpiezoelectric element 214 for electrical isolation. To address thisconcern, in some embodiments the acoustic matching layer 212 is anelectrical insulator, thus reducing or eliminating the need foradditional electrical insulation.

Attention now turns to the integrated transducer assembly 210. FIG. 5illustrates a perspective view of a transducer assembly 210 inaccordance with embodiments of the invention. The transducer assembly210 comprises an elongated outer housing 501 having an axis 505 alongits elongated direction. In some embodiments, the elongated outerhousing 501 comprises a first portion 500 and a second portion 502, eachhaving a common axis 505. In these embodiments, the second portion 502telescopically couples to the first portion 500, such that the firstportion 500 and second portion 502 may move relative to teach other inan axial direction. Further, the elongated outer housing 501 may becylindrical in shape, but other shapes may be equivalently used.

In embodiments where the elongated outer housing 501 comprises a firstportion 500 and second portion 502, the outside diameter of the secondportion 502 at the crystal or distal end 518 is substantially the sameas the first portion 500. However, the second portion 502 also comprisesa reduced diameter portion 520, which telescopes within the internaldiameter of the first portion 500, and thus has an outside diameterslightly smaller than the inside diameter of the first portion 500. Insome embodiments, the length of engagement of the first and secondportions 500 and 502 is approximately equal to the outside diameter, butlonger and shorter engagements may be equivalently used. The outsidediameter of the elongated outer housing 501 is slightly smaller than theinside diameter of the transducer housing 208, which helps ensure thepiezoelectric element location is accurately known.

In accordance with some embodiments, the second portion 502 is made ofplastic (e.g., Ultem 1000). In these embodiments the axial length of thesecond portion 502 is reduced (in comparison to the axial length of thefirst portion 500, which is preferably metallic) because the shorterlength lowers manufacturing cost, but also when made of a plasticmaterial the second portion 502 tends to absorb moisture and swell.Swelling of the second portion 502 is tolerable, and reducing the axiallength of the second portion 502 enables removal of the transducerassembly 210 from the transducer housing 208 in spite of swelling.

Relative rotational movement of the first and second portions 500 and502 and axial displacement are restricted by a pin 506 extendingradially from the second portion 502 through an aperture 504 in thefirst portion 500. In some embodiments, three such pin and aperturecombinations are used, but as few as one and greater than three of thepin and aperture combinations may be equivalently used. Alternatively,the second portion 502 may be designed to have a protrusion thatinteracts with the aperture 504 as an integral part of the secondportion 502.

While the piezoelectric element 214 couples to and at least partiallyoccludes the first end 503 of the elongated outer housing 501,electrical pin holder 508 couples to and at least partially occludes asecond end 509 of the elongated outer housing 501. The elongated outerhousing 501 first portion 500 may comprise connection key 514, whichhelps ensure the integrated transducer assembly is properly oriented forcoupling with the connector 204 key slot. Electrical pin holder 508 maycomprise a slot 515 which engages the connection key 514 preventingrotation of the electrical pin holder 508 within the elongated outerhousing 501. Additionally, the electrical pin holder 508 may furthercomprise an anti-rotation slot 516 which, in combination with a tab onthe transducer housing 208, keeps the integrated transducer assembly 210from rotating in the transducer housing 208. The second end 509 of theelongated outer housing 501 has an internal diameter that is a slidingfit to a small outside diameter of the pin holder 508. The pin holder508 may desirably be made from Ultem 1000, but any rigid, non-conductingmaterial can be used.

FIG. 6 illustrates a perspective cross-sectional view of the transducerassembly 210. In at least some embodiments, the piezoelectric element214 is electrically isolated from the transducer housing 208, and thusat least the second portion 502 is made of a rigid non-conductingmaterial as discussed above. The inside diameter of the elongated outerhousing 501 and the outside diameter of the piezoelectric element 214are selected such that there is space between the transducer assembly210 and the transducer housing 208 into which the transducer assembly210 is inserted. This space provides room for clearance for the meniscus304 (of FIGS. 3 and 4) of the acoustic matching layer. This space alsoprovides room for excess oil or grease that may be applied to thepiezoelectric element's 214 exterior surface prior to insertion into thetransducer housing 208 in order to improve acoustic coupling of thepiezoelectric element 214 and acoustic matching layer 212.

A shoulder 600 in the elongated outer housing 501 abuts thepiezoelectric element 214 to resist axial movement of the piezoelectricelement, such as axial movement caused by forces imparted when thetransducer assembly 210 is mounted within the transducer housing 208.The volume behind the piezoelectric element 214 comprises a backmatching layer 602 (e.g., epoxy, powder-filled epoxy, rubber,powder-filled rubber), and serves several purposes. For example, theback matching layer couples the piezoelectric element 214, and one ormore wires attached to the piezoelectric element 214, to the elongatedouter housing 501. In particular, the mass of the back matching layerimproves the acoustic output of the piezoelectric element 214 byreducing ringing and increasing bandwidth of the acoustic signal. Insome embodiments, the length of the back matching layer (measured alongthe axis of the elongated outer housing) is selected such that the roundtrip travel time of an ultrasonic signal in the back matching layer 602occurs at a time greater than the time of measurement of a receivedsignal. For example, if the fourth zero crossing in the received signalis used as the measurement point, then the round trip travel time wouldpreferably be greater than two cycles at the center frequency ofoperation of the piezoelectric element. Alternatively, the length of theback matching layer 602 is from about 1 to about 9 wavelengths of soundin the back matching layer at the center frequency of operation of thepiezoelectric element. The appropriate length ensures that any reflectedacoustic signals do not arrive at the piezoelectric element during theultrasonic meter's signal transit timing.

Considering further the elongated outer housing 501 comprising a firstportion 500 and second portion 502, the reduced diameter portion 520 ofthe second portion 502 comprises a shoulder 608. The shoulder is smallenough to allow passage for wires through an aperture therein, and toallow an opening for injecting the back matching layer 602. The backmatching layer may be injected with a syringe with a small plastic tip.Chamfers are provided on the ends of this shoulder 608 to ensure nosharp edge is created which could damage wires. The shoulder 608 is alocation upon which a biasing mechanism (discussed below) may push whenbiasing the second portion 502.

In embodiments where the elongated outer housing 501 comprises a firstportion 500 and second portion 502 that are allowed to move axiallyrelative to each other, the transducer assembly 210 comprises a biasingmechanism, such as spring 610. The biasing mechanism biases the firstportion 500 and second portion 502 away from each other along the commonaxis X. The force with which the biasing mechanism biases the firstportion 500 and second portion 502 away from each other is, in someembodiments, from about 4 to about 12 pounds. In alternativeembodiments, the biasing mechanism may be any mechanism to provide thebiasing force, such as a washer, a piece of rubber, or combinations ofsprings, washers and/or pieces of rubber.

Spring 610 is slightly compressed against shoulder 618 during assemblyand at least one pin (partially shown at 506) an aperture combination(FIG. 5) limit axial and rotational movement of the second portion 502within the first portion 500. Once the transducer assembly 210 isinstalled the transducer housing 208, the retaining nut 206 (FIG. 2)further compresses the spring 610. This compression compensates for thetolerances of the assembled parts to ensure that the exterior side ofthe piezoelectric element 214 is in good contact to the interior side312 of the acoustic matching layer 212 (FIG. 4). Once the connector 204(FIG. 2) is assembled the spring 610 may be compressed further. Thespring force may be on the order of 4.9 pounds once the connector 204 isin place. In alternative embodiments, the connector 204 need not applyfurther compressive force on the spring. In embodiments where theelongated outer housing 501 is a single structure, the force to ensuregood coupling between the piezoelectric element 214 and the acousticmatching layer 212 (FIG. 4) may be supplied by the retaining nut 206(FIG. 2) and/or the connector 204 (FIG. 2).

The pin holder 508 holds two connection pins 610 and 612 at the desiredspacing and exposed length. The pins mate with the connector 204,providing electrical connection of the transducer assembly with theelectronics of the meter. Electrical pin 610 couples to thepiezoelectric element 214 by way of a first wire 611 that runs throughthe interior of the elongated outer housing 501 Likewise, second pin 612couples to the piezoelectric element 214 by way of second wire 613 thatalso runs through the interior of the housing 501. In some embodiments,multi-strand copper wire with PTFE insulation is used for wires 611,613, but other types of wire may be equivalently used. In order to holdthe wires 611 and 613 in place, as well as possibly the resistor 614(discussed below) and electric pin holder 508, an adhesive 609 such asepoxy is inserted through the epoxy fill port 612. In some embodiments,the connection pins 610 and 612 are robust gold plated brass pins whichhave solder connection pockets, but other pins may be equivalently used.Two different colors of wire insulation are used to ensure the correctpolarity of the crystal faces and connection pin orientation with theconnection key on the case are maintained during manufacturing. Thewires are twisted during assembly to ensure that any induced electricalsignals in the wires are equalized to avoid such signals frominterfering with crystal impulses during measurement cycles.

A one mega ohm resistor 614 couples between the pins 610 and 612, thuscoupling the two electrode plated faces (discussed below) of thepiezoelectric crystal. This resistor 614 provides a short at lowfrequencies to discharge any electrical energy generated by mechanicalshock or temperature changes during transportation or installation. Atthe high frequency (˜1 MHz) of operation of the transducer, the resistor614 has virtually no effect on the electrical signal sent to orgenerated by the piezoelectric crystal. One lead of the resistor isinsulated by insulation tubing to avoid shorting of this lead to thecase during manufacturing. Alterative transducer designs may compriseadditional electrical components within the integrated transducerassembly (e.g., inductors, amplifiers, switches, zener diodes, orcapacitors). The use of these components may be individually or in manycombinations.

FIGS. 7A and 7B illustrate electrical coupling to the piezoelectricelement 214 in accordance with embodiments of the invention. In someembodiments, the piezoelectric element 214 is a piezoelectric crystal,such as PZT-5A or other similar material. The thickness and diameter ofthe crystal controls the frequency of the ultrasonic signal that isemitted. The exterior side 700 is the side of the piezoelectric element214 that couples to the acoustic matching layer (FIGS. 3 and 4). Theexterior side 700 and interior side 702 of the piezoelectric element areat least partially plated with silver or other metals to createelectrode surfaces. A portion 704 of the plating on the exterior side700 extends around the periphery of the crystal to the interior side702. The plating of the exterior side 700 (comprising the portion 704)and the plating of the interior side 702 are electrically isolated by aregion 706 having no plating. Plating in this manner enables coupling ofboth wires 611 and 613 to the interior side 702 of the piezoelectricelement 214. The plating arrangement as illustrated allows the exteriorside 700 to be flat for good contact to the acoustic matching layer.Alternatively, one wire may extend around the piezoelectric element andcouple to the exterior side 700. In these embodiments, a portion of thehousing 501 (FIGS. 5 and 6) is notched to allow passage of the wire.Moreover, in these embodiments where one of the wires couples directlyto the exterior surface 700, the acoustic matching layer 214 is notchedto accommodate the wire. In yet further embodiments, a first wirecouples to the interior side 702 of the piezoelectric element and thesecond wire couples to the periphery or edge of the piezoelectricelement.

The transducer assembly 210 design greatly simplifies transducerassembly installation and replacement, particularly at pipelinefacilities where conditions (lightning, weather, and the like) are lessthan ideal. Referring to the flow diagram in FIG. 8, in variousembodiments a method 800 of replacing the transducer assembly comprisesdisconnecting the wiring harness (block 802) that electronically couplesthe electronics of the ultrasonic meter (FIGS. 1A-C) to the transducerassembly 210. If used, the biasing mechanism is disengaged (block 803),such as by loosening and removing nut 206 (FIG. 2). Thereafter, thetransducer assembly 804 is removed as a single unit (block 804) from thetransducer housing 208. A replacement transducer assembly is insertedinto the transducer housing (block 806), again as a single unit. In someembodiments, the biasing mechanism is engaged (block 807), such as byinstalling retaining nut 206. Finally, the wiring harness is reconnected(block 808).

While various embodiments of this invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit or teaching of this invention. Theembodiments described herein are exemplary only and are not limiting.Accordingly, the scope of protection is not limited to the embodimentsdescribed herein, but is only limited by the claims which follow, thescope of which shall include all equivalents of the subject matter ofthe claims.

1. A transducer assembly comprising: an elongated outer housingcomprising: a first portion and a second portion, wherein the secondportion telescopically couples to the first portion; and a biasingmechanism coupled to the elongated outer housing, wherein the biasingmechanism is configured to bias the first portion and second portionaway from each other along an axis in an elongated direction of thehousing; a piezoelectric element coupled to and at least partiallyoccluding a first end of the elongated outer housing; a pin holdercoupled to and at least partially occluding a second end of theelongated outer housing, the pin holder comprising a first electricalpin; and a first wire that couples the first electrical pin to thepiezoelectric element, wherein the first wire runs through the interiorof the elongated outer housing.
 2. The assembly of claim 1 wherein thebiasing mechanism is configured to supply a force from about 4 to about12 pounds.
 3. The assembly of claim 1 wherein the biasing mechanismfurther comprises a spring.
 4. A transducer assembly comprising: anelongated outer housing comprising: a first portion and a secondportion, wherein the second portion telescopically couples to the firstportion; an aperture through the first portion; and a pin extendingradially outward from the second portion, the pin extending through theaperture; wherein the pin and the aperture are configured to limittelescopic movement of the first portion relative to the second portion;a piezoelectric element coupled to and at least partially occluding afirst end of the elongated outer housing; a pin holder coupled to and atleast partially occluding a second end of the elongated outer housing,the pin holder comprising a first electrical pin; and a first wire thatcouples the first electrical pin to the piezoelectric element, whereinthe first wire runs through the interior of the elongated outer housing.5. A transducer assembly comprising: an elongated outer housing definingan interior and an exterior, the elongated outer housing having an axisalong its elongated direction; a piezoelectric element coupled to and atleast partially occluding a first end of the elongated outer housing; apin holder coupled to and at least partially occluding a second end ofthe elongated outer housing, the pin holder comprising a firstelectrical pin and a second electrical pin; a first wire that couplesthe first electrical pin to the piezoelectric element, wherein the firstwire runs through the interior of the elongated outer housing; a secondwire that couples the second electrical pin to the piezoelectricelement; and a notch in the elongated outer housing to accommodate oneor more wires coupled to an exterior side of the piezoelectric element.6. An ultrasonic meter comprising: a spool piece with an internal flowpath for a measured fluid; at least two transducer housings inoperational relationship in the spool piece; and a transducer assemblycoupled to one of the at least two transducer housings, wherein thetransducer assembly comprises: an elongated outer housing comprising afirst portion and a second portion, the second portion telescopicallycouples to the first portion along an axis, and wherein the elongatedouter housing defines an interior, an exterior, and the axis along itselongated direction; a piezoelectric element coupled to and at leastpartially occluding a first end of the elongated outer housing; a pinholder coupled to and at least partially occluding a second end of theelongated outer housing, the pin holder comprising a first electricalpin; a first wire that couples the first electrical pin to thepiezoelectric element, wherein the first wire runs through the interiorof the elongated outer housing; and a biasing mechanism coupled to theelongated outer housing, wherein the biasing mechanism biases the firstportion and second portion away from each other along the axis.
 7. Theultrasonic meter of claim 6 wherein the biasing mechanism is oneselected from the group consisting of: a spring; a washer; a piece ofrubber; or combinations thereof.